The present disclosure relates to a memory device in which information is recorded in a memory element based on spin torque magnetization reversal.
Along with the great strides of various information apparatuses from a mobile terminal to a large-capacity server, further high performance such as highly increased integration, speed-up, or low power consumption promotion is sought in elements such as a memory and a logical element composing these information apparatuses.
In particular, the progress of semiconductor nonvolatile memories is remarkable, and flash memories as large-capacity file memories become popular as if the flash memories drive out hard disc drives.
On the other hand, the semiconductor nonvolatile memories are being advanced while the development to a code storages and further working memories is anticipated in order to replace NOR (Not OR) flash memories, DRAMs (Dynamic Random Access Memory) and the like which are generally used at the present time with the semiconductor nonvolatile memories. For example, a Ferroelectric Random Access Memory (FeRAM), a Magnetic Random Access Memory (MRAM), a Phase-Change RAM (PCRAM), and the like are given as the semiconductor nonvolatile memories. A part of them has already been put into practical use.
High-speed rewrite and approximately infinite (1015 times or more) rewrite are possible in the MRAM of these nonvolatile memories because data is stored in the MRAM based on a magnetization direction of a magnetic material. Thus, the MRAMs have already been used in the field of an industrial automation, aircrafts, and the like.
Since the MRAM has a high-speed operation and high reliability, in future, the development of the MRAM to the code storage and the working memory is expected.
However, the MRAM involves a problem in the low power consumption promotion and the large capacity promotion.
This is an essential problem due to the recording principles of the MRAM, that is, a system that a magnetization is reversed by a current magnetic field generated from a wiring.
A recording (that is, magnetization reversal) system not relying on the current magnetic field is studied as one of methods for solving this problem. In particular, the research about spin torque magnetization reversal is actively carried out. The research concerned, for example, is described in U.S. Pat. No. 5,695,864 and Japanese Patent Laid-Open No. 2003-17782.
A memory element utilizing the spin torque magnetization reversal is composed of a Magnetic Tunnel Junction (MTJ) similarly to the case of the MRAM.
Also, in the spin torque magnetization reversal-based memory element, when a spin polarized electron passed through a magnetic layer fixed in a certain direction is intended to enter another free magnetic layer (not fixed in direction thereof), a torque is imposed to the another free magnetic layer. In this case, when a current whose value is equal to or larger than a certain threshold value is caused to flow through the memory element, a direction of the magnetization of the free magnetic layer is reversed.
A polarity of the current caused to flow through the memory element is changed, thereby carrying out rewrite of “0” or “1.”
An absolute value of the current for reversal of the magnetization of the free magnetic layer is equal to or smaller than 1 mA in the case of the memory element which is about 0.1 μm in scale. In addition, the scaling is possible because the current value is reduced in proportion to a volume of the memory element.
In addition thereto, there is also obtained an advantage that a cell configuration becomes simple because a word line for generation of a recording current magnetic field which has been necessary for the MRAM in the past is unnecessary.
Hereinafter, the MRAM utilizing the spin torque magnetization reversal will be referred to as the “Spin Torque-Magnetic Random Access Memory (ST-MRAM).”
Large expectation is placed on the ST-MRAM as the nonvolatile memory which makes the low power consumption and the large capacity promotion possible while the advantages of the MRAM that the high speed operation is carried out and the number of times of rewrite is approximately infinite are held.